Tantalum sputtering target and method for preparation thereof

ABSTRACT

Provided is a tantalum sputtering target having a crystal structure in which the (222) orientation is preferential from a position of 10% of the target thickness toward the center face of the target, and a manufacturing method of a tantalum sputtering target, including the steps of forging and recrystallization annealing, and thereafter rolling, a tantalum ingot or billet having been subject to melting and casting, and forming a crystal structure in which the (222) orientation is preferential from a position of 10% of the target thickness toward the center face of the target. As a result, evenness (uniformity) of the film is enhanced, and quality of the sputter deposition is improved.

BACKGROUND OF THE INVENTION

The present invention pertains to a tantalum sputtering target capableof enhancing the evenness (uniformity) of a film and improving thequality of sputter deposition, and a method for manufacturing a tantalumsputtering target having the foregoing properties by performing forging,annealing, rolling processing, heat treatment and so on to a tantalumingot or billet having been subject to melting and casting.

In recent years, the sputtering method for forming a film from materialssuch as metal or ceramics has been used in numerous fields such aselectronics, corrosion resistant materials and ornaments, catalysts, aswell as in the manufacture of cutting/grinding materials and abrasionresistant materials.

Although the sputtering method itself is a well-known method in theforegoing fields, recently, particularly in the electronics field, atantalum sputtering target suitable for forming films of complex shapesand forming circuits is in demand.

Generally, this tantalum target is manufactured by forging and annealing(heat treatment) an ingot or billet formed by performing electron beammelting and casting to a tantalum material, and thereafter performingrolling and finishing processing (mechanical processing, polishing,etc.) thereto.

In this kind of manufacturing procedure, the forging performed to theingot or billet will destroy the cast structure, disperse or eliminatethe pores and segregations, and, by further annealing this,recrystallization will occur, and the precision and strength of thestructure can be improved to a certain degree.

Generally, the ingot or billet subject to melting and casting has acrystal grain size of roughly 50 mm. By performing forging andrecrystallization annealing to the ingot or billet, the castingstructure will be destroyed, and, for the most part, even and fine (100μm or less) crystal grains can be obtained, but there is a problem inthat these coarse crystals will remain even in the final product.

Generally, upon performing sputtering, the finer and more uniform thecrystals of the target, the more even the deposition, and a film havingstable characteristics can be obtained.

Therefore, the existence of irregular crystal grains that are generatedduring forging, rolling or the annealing to be performed thereafter willchange the sputtering rate, and there is a problem in that evenness(uniformity) of the film will be affected, and the quality of sputterdeposition will deteriorate.

Further, if a forged product with strain remaining therein is used asis, the quality will deteriorate, and this must be avoided at all costs.

Meanwhile, when sputtering a tantalum target with a magnetron sputteringdevice, only a certain area along the magnetic line will in particularbecome eroded (generally, the erosion will progress in a donut shape),and this will gradually become steeper together with the progress oferosion up to the end of sputtering.

At portions where erosion progresses in particular, the surface area ofthe target will increase, and the difference in the surface area incomparison to the other areas will become significant. This differencein surface area will become the difference in the sputter rate, and thefilm tends to be formed thick at the substrate (wafer) portionpositioned opposite to the portion with an increased surface area wheresputtering is focused, and, contrarily, the film tends to be formedthinly at portions where sputtering is not as focused.

This not only generates a problem in that an uneven film is formed in asingle wafer, this will also generate a problem in that the filmthickness will vary from the start to end in the plurality of wafers tobe sputtered. In other words, this will lead to the deterioration in theuniformity of sputter deposition.

As a method of improving the uniformity of such sputter deposition, ithas been generally proposed that the structure should be made uniform aspossible, and in particular to align the crystal orientation across theentire thickness direction of the target. Nevertheless, by merelyaligning the crystal orientation, there is a problem in that thedeterioration of the sputtering film uniformity resulting from thevariation in the foregoing surface area could not be resolved.

As a conventional manufacturing method of a tantalum sputtering targetor high purity tantalum, a manufacturing method of high purity tantalumhas been disclosed (e.g., Patent Document 1 below) comprising the stepsof melting and highly purifying a tantalum sputtering target containing500 ppm or less of metallic impurities and K₂TaF₇, reacting the highlypurified K₂TaF₇ with a reducer and obtaining tantalum powder, andreacting this tantalum powder with iodine in a container.

Further, a 99.95 wt % tantalum sputtering target having an equiaxedstructure of (100) and a maximum grain size of 50 microns or lessmanufactured by rolling and forging has also been disclosed (e.g.,Patent Document 2 below).

Moreover, a high purity tantalum target having a fine structure andcapable of uniform sputtering, in particular, a high purity tantalumtarget of a fine structure in which the average crystal grain size is100 μm or less and (111)<uvw> is preferentially orienting evenly towardthe thickness direction of the target has also been disclosed (e.g.,Patent Document 3 below).

Patent Document 1: PC (WO) 2002-516918

Patent Document 2: PC (WO) 2002-518593

Patent Document 3: U.S. Pat. No. 6,331,233

SUMMARY OF THE INVENTION

In order to overcome the foregoing problems, an object of the presentinvention is to provide a tantalum sputtering target capable ofenhancing evenness (uniformity) of the film and improving the quality ofsputter deposition upon sputtering as a result of improving thestructure of the crystal orientation of the target, and improving andelaborating the forging, rolling and heat treatment processes formanufacturing such improved target, as well as a method of stablymanufacturing such a target.

The present invention provides:

-   1. A tantalum sputtering target comprising a crystal structure in    which the (222) orientation is preferential from a position of 30%    of the target thickness toward the center face of the target;-   2. A tantalum sputtering target comprising a crystal structure in    which the (222) orientation is preferential from a position of 20%    of the target thickness toward the center face of the target;-   3. A tantalum sputtering target comprising a crystal structure in    which the (222) orientation is preferential from a position of 10%    of the target thickness toward the center face of the target;-   4. A tantalum sputtering target according to any one of paragraphs 1    to 3 above, comprising a crystal structure in which the (222)    orientation is preferential at a position excluding the peripheral    edge of the target;-   5. A tantalum sputtering target comprising a crystal structure in    which the (222) orientation is preferential in a disc shape at the    center portion of the target;-   6. A tantalum sputtering target according to any one of paragraphs 1    to 4 above, comprising a crystal structure in which the (222)    orientation is preferential in a disc shape at the center portion of    the target;-   7. A tantalum sputtering target according to any one of paragraphs 1    to 6 above, comprising a crystal structure in which the (222)    orientation is preferential at a position immediately beneath the    initial erosion portion of the target or a position of the erosion    portion when sputtering is performed or a position in the vicinity    thereof;-   8. A manufacturing method of a tantalum sputtering target,    comprising the steps of forging and recrystallization annealing, and    thereafter rolling, a tantalum ingot or billet having been subject    to melting and casting, and forming a crystal structure in which    the (222) orientation is preferential from a position of 10% of the    target thickness toward the center face of the target;-   9. A manufacturing method of a tantalum sputtering target according    to paragraph 8 above, wherein formed is a crystal structure in which    the (222) orientation is preferential at a position excluding the    peripheral edge of the target;-   10. A manufacturing method of a tantalum sputtering target according    to paragraph 8 or paragraph 9 above, wherein formed is a crystal    structure in which the (222) orientation is preferential in a disc    shape at the center portion of the target;-   11. A tantalum sputtering target according to any one of paragraphs    8 to 10 above, wherein formed is a crystal structure in which    the (222) orientation is preferential at a position immediately    beneath the initial erosion portion of the target or a position of    the erosion portion when sputtering is performed or a position in    the vicinity thereof;-   12. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 11 above, wherein forging and    recrystallization annealing are repeated two or more times;-   13. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 12 above, wherein kneading is further    performed;-   14. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 13 above, wherein, after forging,    cross rolling and heat treatment are performed to process a tabular    target;-   15. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 14 above, wherein, after forging the    ingot or billet, recrystallization annealing is performed at a    recrystallization temperature of up to 1673K;-   16. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 15 above, wherein, after rolling,    crystal homogenization annealing or straightening annealing is    performed;-   17. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 16 above, wherein the average crystal    grain size of the target is made to be a fine crystal grain size of    80 μm or less; and-   18. A manufacturing method of a tantalum sputtering target according    to any one of paragraphs 8 to 16 above, wherein the average crystal    grain size of the target is made to be a fine crystal grain size of    30 to 60 μm or less.

DETAILED DESCRIPTION OF THE INVENTION

The tantalum sputtering target of the present invention comprises acrystal structure in which the (222) orientation is preferential from aposition of 30% of the target thickness, or a position of 20% of thetarget thickness, or a position of 10% of the target thickness towardthe center face of the target. This position may be suitably adjusted inaccordance with conditions such as the measurement, shape or targetdeposition of the tantalum target.

This yields a structure where the structure of the (222) orientation isspreading in a disc shape (or convex lens shape) at the center of thetarget, and, generally speaking, a crystal structure having apreferential (222) orientation does not exist at the peripheral edge ofthe target.

Although a crystal structure of the (222) orientation may exist up tothe peripheral edge portion, it will be difficult to manufacture atarget, with a favorable yield ratio, upon performing the forging androlling processes described later. Further, since the peripheral edge ofthe target will not erode much and because erosion will not continue upto the late stage of sputtering, the target will not be affected inparticular.

From the structure of the foregoing target, the crystal structure of the(222) orientation will be positioned immediately beneath the initialerosion portion of the target or at the erosion portion when sputteringis performed or in the vicinity thereof.

As described above, after the start of sputtering, although the erosionwill progress roughly along the magnetic line; that is, although theerosion will progress in a donut shape on the planar surface of thetarget, and gradually become steeper, the surface area of the targetwill increase at the portion where erosion is progressing in particular,and the difference of the surface area in comparison to the other areaswill become significant.

This difference in surface area will become the difference in the amountof tantalum to be sputtered; that is, it will become the difference inthe sputter rate, and there is a problem in that the film tends to beformed thick at the substrate (wafer) portion positioned opposite to theportion with an increased surface area where sputtering is focused, and,contrarily, the film tends to be formed thinly at portions wheresputtering is not as focused. This will cause deterioration in theuniformity of sputter deposition.

Nevertheless, with the tantalum target of the present invention having astructure where the structure of the (222) orientation is spreading in adisc shape (or convex lens shape) at the center of the target, it hasbecome clear that the deterioration in uniformity of the sputtering filmcan be considerably reduced. Although this phenomenon has not been fullyclarified, the following can be considered to be the reason therefor.

In other words, when employing the tantalum target of the presentinvention, since it is not the crystal structure of the (222)orientation at the initial stage and (110), (200) and (211) are the mainorientations, erosion will occur at a normal sputtering speed (rate).Since a tantalum target having this kind of orientation has a relativelyfast sputtering speed, the productivity will improve, and it could besaid that this is preferable.

Then, erosion will progress in a donut shape on the target face roughlyalong the magnetic line. This is no different than conventional erosion,and, upon being subject to further erosion, the erosion portion willgradually become steeper.

Further, the sputter rate will change on the planar surface of thetarget as a result of the above, and uniformity of the sputtering filmwill deteriorate.

And, since the rolling of the erosion face will enlarge as describedabove, the target surface area of such portion will increase evenfurther, and deterioration of uniformity tends to increase at anaccelerated pace.

Nevertheless, when employing the tantalum target of the presentinvention, the structure of the (222) orientation will appear on theerosion face midway during the progress of erosion. The structure ofthis (222) orientation is characterized in that the sputter rate is slowin comparison to other orientations.

The meaning of this is extremely significant, and the structure of the(222) orientation appearing midway suppresses the rapid progress ofsteep and uneven (partial) erosion, and, the structure of the (222)orientation having a slow sputter rate offsets the sputter amount oftantalum which increased pursuant to the increase in the surface area,and functions to make the sputter amount; that is, the sputter rateuniform up to the late stage of sputtering. Therefore, the totalthickness of the film formed on the substrate and the film thicknessdistribution within the wafer can be made uniform, and this willfunction to prevent the deterioration of uniformity.

Since the erosion on the target surface is progressing to a certaindegree, the appearance of the target does not seem to be much differentfrom a conventional target. Thus, it has been confirmed that asignificant difference is evident in the uniformity of the deposition.

From which point of the target thickness the crystal structure in whichthe (222) orientation is preferential should be disposed may be changedin accordance with the thickness of the target, the size of the surfacearea or required deposition conditions, and the (222) orientation may bearbitrarily selected from the position of 30% or 20% or 10% of thethickness toward the center face of the target.

It is desirable to make the crystal structure of the (222) orientationin a state where erosion has progressed a certain degree. With a targethaving a uniform structure from the surface toward the center portion,the surface erosion will become uneven as described above and,therefore, it could be said that it is not possible to secure theuniformity of deposition.

The tantalum sputtering target of the present invention is manufacturedwith the following processes. Specifically, foremost, a tantalum rawmaterial (high purity tantalum of 4N5N or higher is ordinarily used) ismelted with electron beam melting or the like, and this is cast toprepare an ingot or billet.

Next, this ingot or billet is subject to a series of processes such ashot forging, cold forging, rolling, annealing (heat treatment),finishing processing and so on such that a crystal structure in whichthe (222) orientation is preferential from a position of 30% of thetarget thickness, or a position of 20% of the target thickness, or aposition of 10% of the target thickness toward the center face of thetarget is formed.

Further, as a result, a crystal structure in which the (222) orientationis preferential in a disc shape may be formed at the center portion ofthe target; that is, a position immediately beneath the initial erosionportion of the target or a position of the erosion portion whensputtering is performed or a position in the vicinity thereof.

When forming a crystal structure in which the (222) orientation ispreferential at the center portion of the target by performing forging,recrystallization annealing and rolling processing, it is difficult toform a crystal structure in which the (222) orientation is preferentialup to the peripheral edge of the target even upon adjusting theconditions of forging, recrystallization annealing and rollingprocessing.

Although it is possible to cut the portions of the target without any(222) orientation, there is a problem in that the yield rate willdeteriorate. Nevertheless, since this peripheral edge hardly erodes, andis not a portion that will in particular affect the deposition, the(222) orientation may be formed in a disc shape excluding the peripheraledge.

Moreover, with respect to the forging conditions, by repeating forgingand recrystallization annealing two or more times, a tantalum sputteringtarget having the foregoing structure may be manufactured efficiently.Further, sufficient forging is required for forming a crystal structurein which the (222) orientation is preferential, and kneading whichrepeats upset forging and extend forging is in particular effective.

In addition, it is effective to perform cross rolling (multi-directionrolling) and heat treatment after forging in order to prepare a tabulartarget.

As the annealing condition, after forging the ingot or billet, it isdesirable to perform recrystallization annealing at a recrystallizationtemperature of up to 1673K. Although recrystallization annealing may beperformed once at a recrystallization temperature of 1673K, a desiredcasting structure may be effectively obtained by repeating suchrecrystallization annealing process twice.

The temperature loss is significant and wasteful when the annealingtemperature exceeds 1673K, and it is desirable that that the temperaturebe 1673K or lower.

As a result, a tantalum sputtering target comprising a crystal structurein which the (222) orientation is preferential from a position of 30% ofthe target thickness, or a position of 20% of the target thickness, or aposition of 10% of the target thickness toward the center face of thetarget may be obtained, and a tantalum sputtering target having anaverage crystal grain size of 80 μm or less, and even a fine crystalgrain size of 30 to 60 μm may also be manufactured.

When performing sputtering with the target of the present invention,evenness (uniformity) of the film can be further enhanced, and qualityof the sputter deposition may be further improved.

EXAMPLES AND COMPARATIVE EXAMPLES

The present invention is now explained in detail with reference to theExamples. These Examples are merely illustrative, and the presentinvention shall in no way be limited thereby. In other words, thepresent invention shall only be limited by the scope of claim for apatent, and shall include the various modifications other than theExamples of this invention.

Example 1

A tantalum raw material having a purity of 99.997% was subject toelectron beam melting, and this was cast to prepare an ingot having alength of 1000 nm and diameter of 200 mmφ. The crystal grain size inthis case was approximately 50 mm. Next, this ingot was subject to coldtightening forging and made to be 110 mmφ, thereafter cut into a billethaving a thickness of 110 mm and a diameter of 110 mmφ. This billet wassubject to cold kneading, and thereafter subject to recrystallizationannealing at a temperature of 1173K, cold kneading was performed theretoonce again, and recrystallization annealing was also performed at atemperature of 1173K once again.

Next, the forged ingot was subject to cold rolling (multi direction),and straightening and recrystallization processing (heat treatment) wasperformed at 1173K to obtain a target raw material having a thickness of10 mm and 350 mmφ, and mechanical finishing processing was performedthereto to obtain a target material having a thickness of 6.35 mm and320 mmφ.

With the foregoing processes, obtained was a tantalum target superior inuniformity comprising a crystal structure in which the (222) orientationwas preferential from a position of 30% of the target thickness towardthe center face of the target, and having a fine crystal grain size inwhich the average crystal grain size was 45 μm. When performingsputtering with this tantalum target, evenness (uniformity) of the filmwas favorable, and quality of the sputter deposition improved. Theresults are shown in Table 1.

Incidentally, since the sheet resistance depends on the film thickness,distribution of the sheet resistance within the wafer (8 inch) wasmeasured, and the status of film thickness distribution was examinedthereby. Specifically, the sheet resistance at 49 points on the waferwas measured, and the standard deviation (σ) was calculated.

As evident from Table 1, in Example 1, variation in the resistancedistribution within the sheet from the initial stage of sputtering tothe late stage of sputtering was small; that is, variation in the filmthickness distribution was small.

TABLE 1 Transition (1σ) of Sheet Resistance Distribution in Wafer (8Inch) Comparative Comparative Example 1 Example 2 Example 3 Example 1Example 2 (222) Orientation Position  30%  10%  20% — — from SurfaceInitial Stage of Sputtering 4.5% 4.8% 4.4% 4.3% 4.8% Mid Stage ofSputtering 5.5% 4.4% 5.1% 6.5% 7.2% Late Stage of Sputtering 5.1% 4.7%5.0% 11.2% 11.5%

Example 2

A tantalum raw material having a purity of 99.997% was subject toelectron beam melting, and this was cast to prepare an ingot having alength of 1000 nm and diameter of 200 mmφ. The crystal grain size inthis case was approximately 55 mm. Next, this ingot was subject to coldtightening forging and made to be 110 mmφ, thereafter cut into a billethaving a thickness of 110 mm and a diameter of 110 mmφ. This billet wassubject to cold kneading, and thereafter subject to recrystallizationannealing at a temperature of 1523K, cold kneading was performed theretoonce again, and recrystallization annealing was also performed at atemperature of 1523K once again.

Next, the forged ingot was subject to cold rolling (multi direction),and straightening and recrystallization processing (heat treatment) wasperformed at 1523K to obtain a target raw material having a thickness of10 mm and 350 mmφ, and mechanical finishing processing was performedthereto to obtain a target material having a thickness of 6.35 mm and320 mmφ.

With the foregoing processes, obtained was a tantalum target superior inuniformity comprising a crystal structure in which the (222) orientationwas preferential from a position of 10% of the target thickness towardthe center face of the target, and having a fine crystal grain size inwhich the average crystal grain size was 80 μm. When performingsputtering with this tantalum target, evenness (uniformity) of the filmwas favorable, and quality of the sputter deposition improved. Theresults are similarly shown in Table 1.

Incidentally, since the sheet resistance depends on the film thickness,distribution of the sheet resistance within the wafer (8 inch) wasmeasured, and the status of film thickness distribution was examinedthereby. Specifically, the sheet resistance at 49 points on the waferwas measured, and the standard deviation (σ) was calculated.

The results shown in Example 2 of Table 1 were obtained by measuring thesheet resistance at 49 points on the wafer as with Example 1, andcalculating the standard deviation (σ) thereof. In Example 2, variationin the resistance distribution within the sheet from the initial stageof sputtering to the late stage of sputtering was small; that is,variation in the film thickness distribution was small.

Example 3

A tantalum raw material having a purity of 99.997% was subject toelectron beam melting, and this was cast to prepare an ingot having alength of 1000 nm and diameter of 200 mmφ. The crystal grain size inthis case was approximately 55 mm. Next, this ingot was subject to coldtightening forging and made to be 110 mmφ, thereafter cut into a billethaving a thickness of 110 mm and a diameter of 110 mmφ. This billet wassubject to cold kneading, and thereafter subject to recrystallizationannealing at a temperature of 1373K, cold kneading was performed theretoonce again, and recrystallization annealing was also performed at atemperature of 1373K once again.

Next, the forged ingot was subject to cold rolling (multi direction),and straightening and recrystallization processing (heat treatment) wasperformed at 1373K to obtain a target raw material having a thickness of10 mm and 350 mmφ, and mechanical finishing processing was performedthereto to obtain a target material having a thickness of 6.35 mm and320 mmφ.

With the foregoing processes, obtained was a tantalum target superior inuniformity comprising a crystal structure in which the (222) orientationwas preferential from a position of 20% of the target thickness towardthe center face of the target, and having a fine crystal grain size inwhich the average crystal grain size was 60 μm. When performingsputtering with this tantalum target, evenness (uniformity) of the filmwas favorable, and quality of the sputter deposition improved. Theresults are similarly shown in Table 1.

The results shown in Example 3 of Table 1 were obtained by measuring thesheet resistance at 49 points on the wafer (8 inch) as with Example 1,and calculating the standard deviation (σ) thereof. In Example 3,variation in the resistance distribution within the sheet from theinitial stage of sputtering to the late stage of sputtering was small;that is, variation in the film thickness distribution was small.

Comparative Example 1

A tantalum raw material having a purity of 99.997% was subject toelectron beam melting, and this was cast to prepare an ingot having alength of 1000 mm and diameter of 200 mmφ. The crystal grain size inthis case was approximately 50 mm. Next, this ingot was subject to coldtightening forging and made to be rectangle having a width of 350 mm,height of 85 mm and length of 1000 mm, thereafter cut into a billethaving a length of 80 mm, width of 350 mm and height of 85 mm. Thisbillet was subject to recrystallization annealing at a temperature of1173K, thereafter extended to a length of 700 mm by performing coldunidirectional rolling, and straightening and recrystallizationannealing was performed at a temperature of 1173K to obtain two sheetsof a target raw material having a thickness of 10 mm and 350 mmφ, andmechanical finishing processing was performed thereto to obtain a targetmaterial having a thickness of 6.35 mm and 320 mmφ.

With the tantalum target obtained with the foregoing processes, thecrystal grains were 60 to 120 μm and varied in a layer shape, and becamea tantalum target in which the orientation was mostly aligned from thetarget surface toward the center portion.

When performing sputtering with this tantalum target, evenness(uniformity) of the film was inferior, and caused the quality of sputterdeposition to deteriorate. The results are similarly shown in Table 1.

The results shown in Comparative Example 1 of Table 1 were obtained bymeasuring the sheet resistance at 49 points on the wafer (8 inch) aswith Example 1, and calculating the standard deviation (σ) thereof. InComparative Example 1, variation in the resistance distribution withinthe sheet from the initial stage of sputtering to the late stage ofsputtering was large; that is, variation in the film thicknessdistribution was significant.

Comparative Example 2

A tantalum raw material having a purity of 99.997% was subject toelectron beam melting, and this was cast to prepare an ingot having alength of 1000 mm and diameter of 200 mmφ. The crystal grain size inthis case was approximately 50 mm. Next, this ingot was subject to coldtightening forging and made to be rectangle having a width of 350 mm,height of 85 mm and length of 1000 mm, thereafter cut into a billethaving a length of 80 mm, width of 350 mm and height of 85 mm.

This billet was subject to recrystallization annealing at a temperatureof 1373K, thereafter extended to a length of 700 mm by performing coldunidirectional rolling, and straightening and recrystallizationannealing was performed at a temperature of 1373K to obtain two sheetsof a target raw material having a thickness of 10 mm and 350 mmφ, andmechanical finishing processing was performed thereto to obtain a targetmaterial having a thickness of 6.35 mm and 320 mmφ.

With the tantalum target obtained with the foregoing processes, thecrystal grains were 80 to 150 μm and varied in a layer shape, and becamea tantalum target in which the orientation was mostly aligned from thetarget surface toward the center portion.

When performing sputtering with this tantalum target, evenness(uniformity) of the film was inferior, and caused the quality of sputterdeposition to deteriorate. The results are similarly shown in Table 1.

The results shown in Comparative Example 2 of Table 1 were obtained bymeasuring the sheet resistance at 49 points on the wafer (8 inch) aswith Example 1, and calculating the standard deviation (σ) thereof. InComparative Example 2, variation in the resistance distribution withinthe sheet from the initial stage of sputtering to the late stage ofsputtering was large; that is, variation in the film thicknessdistribution was significant.

The present invention yields a significant effect of enhancing evenness(uniformity) of the film and improving quality of the sputteringdeposition by providing a crystal structure in which the (222)orientation is preferential from a position of 30% of the targetthickness, or a position of 20% of the target thickness, or a positionof 10% of the target thickness toward the center face of the target andby forming a crystal structure in a disc shape (convex lens shape) atthe center of the target.

1. A sputtering target comprising a tantalum sputtering target having acrystal structure in which the (222) orientation is preferential in adisc shape or convex lens shape at a center portion of the target andnot preferential in a remainder peripheral portion of the target.
 2. Asputtering target according to claim 1, wherein said (222) orientationof said crystal structure is preferential at a position selected from aposition immediately beneath an initial erosion portion of the target, aposition of an erosion portion of the target when sputtering isperformed, and a position in a vicinity thereof.
 3. A sputtering targetaccording to claim 1, wherein said target has a body produced as aresult of melting and casting a tantalum raw material.